For at least the last hundred years, the world's most dynamic religion has been neither Christianity nor Islam.

It is leftism.

Most people do not recognize what is probably the single most important fact of modern life. One reason is that leftism is overwhelmingly secular (more than merely secular: it is inherently opposed to all traditional religions), and therefore people do not regard it as a religion. Another is that leftism so convincingly portrays itself as solely the product of reason, intellect, and science that it has not been seen as the dogma-based ideology that it is. Therefore, the vast majority of the people who affirm leftist beliefs think of their views as the only way to properly think about life.

That, in turn, explains why anyone who opposes leftism is labeled anti-intellectual, anti-progress, anti-science, anti-minority and anti-reason (among many other pejorative epithets): leftists truly believe that there is no other way to think.

How successful has leftism been?

It dominates the thinking of Europe, much of Latin America, Canada, and Asia, as well as the thinking of the political and intellectual elites of most of the world. Outside of the Muslim world, it is virtually the only way in which news is reported and virtually the only way in which young people are educated from elementary school through university.

Only the United States, of all Western countries, has resisted leftism. But that resistance is fading as increasing numbers of Americans abandon traditional Judeo-Christian religions, lead secular lives, are educated by teachers whose views are almost uniformly left-wing and are exposed on a daily basis virtually exclusively to leftist views in their news and entertainment media.

And when there is resistance, the left declares it "extremist." Merely believing that marriage should remain defined as it has been throughout recorded history, as between a man and a woman, renders you an extremist. So, too, belief that government should be small -- the Tea Party position -- renders one an extremist. Last week, the managing editor of Time Magazine, Richard Stengel, said on MSNBC that the Salafis, the most radical Islamist sect, are "the Tea Party of Muslim democracy."

Even Christianity and Judaism, the pillars of Judeo-Christian values, the moral value system upon which America was founded and thanks to which it became the world's beacon of liberty, have been widely influenced by leftism. Many priests, ministers, rabbis and many Jewish and Christian seminaries are leftist in content and Jewish or Christian only in form.

Years ago, I debated one of the most prominent rabbis in the Conservative movement of Judaism on the issue of whether morality must be God-based. The Ivy League Ph.D., yarmulke-wearing rabbi argued that God was not morally necessary. If you want to understand why so many Jews vote left while nearly all the Western world's opposition to -- and frequently hatred of -- Israel emanates from the left, one explanation is this: For most American Jews, their religion is leftism, while Judaism is their ethnicity and culture. The Reform, and increasingly the Conservative, movements have, to a large extent, become political movements that use Hebrew and Jewish rituals to equate Judaism with progressive politics.

Within mainstream Protestantism and Catholicism, the same dominance of leftist values exists. The United States Conference of Catholic Bishops largely holds the same social and economic views as the Democratic Party and The New York Times editorial page. It differs with the left with regard to same-sex marriage, abortion and religious freedom issues such as those pertaining to Catholic hospitals and government-funded contraception. As for mainstream Protestant denominations, they, too, are largely indistinguishable from leftism. Proof? Ask a liberal Protestant minister to name one important area in which he and leftism differ. Ask a liberal Reform or Conservative rabbi the same question. Their silence will be telling.

The truth is that the left has been far more successful in converting in converting Jews and Christians to Leftism than Christianity and Judaism have been in influencing leftists to convert to Christianity or Judaism.

Finally, leftism has even attained considerable success at undoing the central American values of liberty, "In God We Trust," and "E Pluribus Unum," supplanting liberty with egalitarianism, a God-based society with secularism, and "E Pluribus Unum" with multiculturalism. (I make this case at length in "Still the Best Hope: Why the World Needs American Values to Triumph" [HarperCollins].)

This triumph of the twentieth century's most dynamic religion -- leftism -- is why, even in the midst of an ongoing recession, the leftist candidate may win. As I wrote in my last column, it's not just the economy, stupid.

Dennis Prager's latest book, "Still the Best Hope: Why the World Needs American Values to Triumph," was published April 24 by HarperCollins. He is a nationally syndicated radio show host and creator of PragerUniversity.Com.